Hearing-impaired people often have difficulty comprehending speech in noisy and/or reverberant environments such as encountered at parties or in a restaurant. The hearing-impaired person may have difficulty comprehending the speech of the talkers due to: 1) a hearing aid that may not adequately correct for the loss of hearing sensitivity to quiet sounds, or 2) a residual hearing acuity that is inadequate to permit that person to understand speech in the presence of noise levels that normal-hearing individuals find acceptable for carrying on a conversation. The first problem, lack of adequate audibility at some frequencies, can often be corrected with readjustment or change in the hearing aid circuit. The second problem, lack of adequate acuity, cannot be corrected with any known circuit. More specifically, those with normal hearing can carry on a conversation at a signal-to-noise ratio (SNR) of 0 to −5 dB, meaning the noise may be as much as 5 dB more intense than the desired speech signal. Individuals with moderate-to-severe hearing loss, on the other hand, may often require an SNR of +5 to +10 dB, 10 dB greater than those with normal hearing. The impossibility of a circuit solution to the problem is seen, for example, by the fact that no circuit can know which of many voices at a party is noise and which is considered signal. It is well known that a listener can switch his or her attention at will from one talker to another at a noisy party, often while continuing to look at the original uninteresting talker. These and other considerations are discussed in more detail in an editorial “Hearing Aids: Past, Present, and Future,” by Mead C. Killion, scheduled to appear in the May 1997 issue of the British Journal of Audiology.
The SNR problem has been most obvious with children having severe-to-profound hearing loss. Such children find it impossible to properly understand the teacher even when they wear the best conventional hearing aids in a typical classroom. The use of FM systems such as those currently available from manufacturers like Telex of Minnesota and others has provided a substantially improved SNR for such children, permitting them to learn and understand speech in classroom settings.
In FM systems, the teacher's voice (or other audio signal, perhaps from a video tape or audio recording) is used to frequency modulate a radio frequency carrier which is transmitted within the classroom. The students are then equipped with FM receivers. The FM receivers pick up the transmitted signal, demodulate it, and present received audio either to the students' hearing aids or to their ears via headphones or earphones. In this particular example, there is one audio signal, which is transmitted, that being the teacher's voice.
A severely hearing-impaired adult at a restaurant may face a similar difficulty with respect to noise, but now at least three talkers (assuming the case where two couples go out to eat) need to be heard. Passing a single microphone around is sometimes done as an effective, but inconvenient, solution. Similarly, head-worn hearing aids including FM receivers used with single-microphone FM transmitters are increasingly being used. One such effective system is manufactured by AVR Communications in Israel.
What is clearly needed, however, is a convenient multiple-microphone pickup system where each microphone operates in a wireless mode. Such a system would serve both those with hearing impairment and normally-hearing individuals, allowing both to communicate in difficult situations and environments. Such systems can be made small enough to also be used by individuals who wish to communicate discreetly with their undercover teammates.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.